The mechanism of action of the direct lymphotoxic effect of 2'-deoxycoformycin is being determined in vitro in concanavalin A-stimulated mouse spleen lymphocytes. Measurements of ribonucleoside mono- and triphosphates, adenosine deaminase activity, methylation and synthesis of RNA and DNA, and the metabolism of 2'-deoxycoformycin will be correlated with the suppression of blasto-genesis. Nucleotide levels and adenosine deaminase activity will be measured in leukemic lymphocytes in patients with chronic lymphocytic leukemia undergoing treatment with 2'-deoxycoformycin.